Getting Started

Below we present examples for getting started in using FedX.

The examples query data from http://dbpedia.org/ and join it with data from https://www.wikidata.org/. It turns out that these endpoints are currently the most reliable ones that are publicly accessible.

Example query

Retrieve the European Union countries from DBpedia and join it with the GDP data coming from Wikidata

SELECT * WHERE { 
  ?country a yago:WikicatMemberStatesOfTheEuropeanUnion .
  ?country owl:sameAs ?countrySameAs . 
  ?countrySameAs wdt:P2131 ?gdp .
}

Note that the query is a bit artificial, however, it illustrates quite well the powers of federating different data sources.

Using a Java program

The following Java code can be used to execute our example query against the federation.

Config.initialize();

FedXRepository repository = FedXFactory.newFederation()
	.withSparqlEndpoint("http://dbpedia.org/sparql")
	.withSparqlEndpoint("https://query.wikidata.org/sparql")
	.create();
		
try (RepositoryConnection conn = repository.getConnection()) {

	String query = 
		"PREFIX wd: <http://www.wikidata.org/entity/> "
		+ "PREFIX wdt: <http://www.wikidata.org/prop/direct/> "
		+ "SELECT * WHERE { "
		+ " ?country a <http://dbpedia.org/class/yago/WikicatMemberStatesOfTheEuropeanUnion> ."
		+ " ?country <http://www.w3.org/2002/07/owl#sameAs> ?countrySameAs . "
		+ " ?countrySameAs wdt:P2131 ?gdp ."
		+ "}";

	TupleQuery tq = conn.prepareTupleQuery(query);
	try (TupleQueryResult tqRes = tq.evaluate()) {

		int count = 0;
		while (tqRes.hasNext()) {
			BindingSet b = tqRes.next();
			System.out.println(b);
			count++;
		}

		System.out.println("Results: " + count);
	}
}
		
repository.shutDown();

The full code is also available as source in the "demos" package of the test source folder.

Instead of defining the federation via code, it is also possible to use data configurations. See also FedX-In-Java for more examples.

Using the CLI

As simple as that, FedX provides a comprehensive command line interface to get started without any prerequisites. Just start the CLI (cli.bat/cli.sh) and access real SPARQL endpoints from the Linked Open Data cloud.

> ./cli.sh -d examples/DBpediaWikidata.ttl @q examples/q_gettingStarted.txt

See also Using the CLI for detailed documentation.